Field of the Invention
The present invention relates to hole sealing means for sealing opposing holes in spaced apart walls and, more particularly, to such sealing means for use in sealing borescope holes in gas turbine engines.
Gas turbine engines incorporate structures, such as casings which operate in very hot environments which causes the structures to undergo differential thermal growth. The engines often include spaced apart walls or casings having opposing holes which require removable sealing means. For example, in the aircraft engine industry, many engines include double walled structures, such as compressors and combustors, wherein the outer and inner walls are respectively provided with opposing holes. One purpose of such opposing holes is to allow inspection and monitoring of the engine. This may be accomplished by inserting inspection equipment, such as borescopes and/or probes, through such holes. Examples of such inspection apparatus can be found in U.S. Pat. No. 3,362,160 entitled, "Gas Turbine Engine Inspection Apparatus" issued to Bourgeois on Jan. 9, 1968; in U.S. Pat. No. 4,300,774 entitled, "Removable sealing plug for spaced apart wall structure", issued to Hollis et al. on Nov. 17, 1981; and in U.S. Pat. No. 4,815,276, entitled, "Borescope Plug" issued to Hansel et al. Mar. 28, 1989; all of which are hereby incorporated by reference.
The problem with the prior art is that the single borescope plug sealing apparatus does not accommodate differential thermal growth between the two casings very well. The inner casing, which is subjected to greater temperatures than the outer casing, experiences a different amount of thermal growth so that the spaced apart holes become misaligned during engine operation causing seal leakage. This may allow hot gases to flow into passageways such as a bypass duct which was not designed to contain hot gases which in turn may lead to a loss of structural integrity. Furthermore, the leakage can cause decreased power capability and lower fuel efficiency. Borescope plugs also interfere with gas stream between the two casings and therefore cause aerodynamic problems which further decreases the efficiency of the engine.
Accordingly, it is a general object of this invention to provide a sealing means for double wall structures subject to differential thermal growth.
Another object of the present invention, is to provide such sealing means with a single easily accessible borescope plug.
Yet another object of the present invention, is to provide such sealing means with a minimal amount of interference with the flow between the two walls.